Chimney flue extension process

Sometimes, the chimney flue needs to be extended to create a better draft. This is needed in situations when smoke builds up more than accepted. The flue must be at least 3 feet higher than the roof.

Tools and materials needed

  • Hammer
  • Chisel
  • Wire Brush
  • Mortar Trowel
  • Caulking gun
  • Terra Cotta Flue Liner extension
  • Fireplace Mortar
  • Mortar
  • Bricks
  • 2×6 wood
  • Plastic sheeting

Chimney crown removal

Use a hammer and chisel to break off the chimney crown. If you have a chimney cap made out of stainless steel or terracotta, you mustn’t damage it. Also, make sure not to damage the flue liner either.

Flue liner extension

Once you’ve exposed the liner, clean off the area with a wire brush. Apply mortar on the top piece of the liner and then place the liner extension over the old one.


Build around the new liner using bricks and mortar. Leave 12 inches of liner to stick out the brick wall.

Chimney crown frame

Build a frame around the brick of the chimney sing 2×6 inch lumber. Fill the space between the frame and the liner with mortar mixture. Use a trowel to model the mortar upward towards the liner. About 4 inches of the liner should remain exposed.


Moisten the area with the mortar and cover it with plastic sheeting. Let it settle for a few days. Make sure it is damp over this type period. Also, do not remove the frame.  After a few days of waiting, remove the frame.

Chimney cap

If you previously removed a chimney cap, you can reinstall it on top of the chimney crown or avoid the crown if your cap is also a crown.

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